thanks, i had wondered if it was a similar principle to stalin's paraffin radios with a hot bit and a cool bit but it is different semis at the same temp .

very clever.

iirc there are fan assisted/ thermoelectric solid fuel (sticks etc )camping stoves that work like the paraffin radio with a hot/cold differential driving the electrons and giving a couple of watts for phones etc while you cook dinner.

using one temp /two semis is far more compact and light and might retro fit to a kelly kettle or perhaps even direct into a fire although the working temp range might be an issue . i had considered the two temp option for a kelly conversion but for the likely weight i recon a pv panel would be a better idea in most camping situations.this way looks light.